Theories of crackling noise

Crackling noise arises when a system responds to changing external conditions through discrete, impulsive events spanning a broad range of sizes. A wide variety of physical systems exhibiting crackling noise have been studied. Earthquakes arise to relieve the strain due to the slow motions of techtonic plates. The slow contraction of your fingers causes a piece of paper to respond with a series of impulsive events as it crumples. Because these impulsive events have smooth statistical distributions over a huge range of sizes, their behaviour is likely to be independent of microscopic and macroscopic details, and progress can be made by the use of simple models.